1. Field of Invention
The present invention relates to a method of introducing an impurity into a wafer surface. More particularly, the present invention relates to a method of introducing an impurity into a wafer surface with low energy implantation and controlled surface removal.
2. Description of Related Art
Ion implantation has been a process of choice to introduce dopant into silicon substrate in advanced CMOS technology. As device continue to be scaled, the need for ultra shallow junction formation becomes increasingly important for the source/drain area. In the production of very small devices, it is necessary to reduce the junction depths. Most of the work in shallow junction formation has concentrated on applying conventional ion implantation to form very shallow source/drain for submicron CMOS.
A great deal of emphasis has been placed on reducing the implant energy. Many manufacturers of ion implant equipment are pushing their systems to a few keV. Some options for forming ultra shallow junctions includes using a layer on top of the silicon as a diffusion source, using a plasma immersion doping as an ion source. However, modern ion implanters are often expensive and present many challenges to form ultra shallow junctions. For example, advanced low energy implanter has to add decelerators to conventional tool set up in order to achieve the proper low energy range. This addition poses challenges in technical parameters and cost. Plasma immersion doping method has the potential for shallow junction formation. However, the dopant dosage is hard to control with high precision, namely, the uniformity of the profile across the wafer is difficult to control. Therefore, a new method of high dose and low energy ion implantation is needed.